1. Field of the Invention
This invention relates to merging and splitting intersecting geometry-only solids and surfaces in an intuitive manner.
2. Prior Art
Objects in a CAD system can be represented in a parameter-based way or in a geometry-based way. In a parameter-based representation, the object is modeled as an object along with a set of features and history that define the object. In a geometry-based representation, the object is simply represented as a set of geometric data.
In modern CAD systems, geometry can be created in three basic ways: from manipulation of 2D sections, creation of edge features by modifications to the sharp boundaries between faces (e.g., a fillet), and combining and manipulating solid primitives using a set of Boolean operations. Over time, every major CAD tool has organized these combinatorial Booleans according to their inputs and desired output. This organization has resulted in many separate workflows located within separate features and tools to perform these functions. Moreover, since these CAD tools essentially force the user to make up a recipe of desired functions, and only then ask for the calculation to occur, the user never knows the result until the operation has concluded. Changes to a model that are made after a completed operation involve rolling the history of the model backwards and redefining the Boolean operation with different selections and/or options. This is a frustrating and time-consuming endeavor.
When editing a previously combined or split solid or surface in a parametric system, the process requires step-by-step re-creation of the original solids and/or surfaces. To modify the combined or split objects, changes must be rolled back, and the new change must be made before a user can return to the current step. This is a consequence of parametric systems having added many history features on top of the actual geometry modeling functionality. These systems have interwoven these features into the software so that making changes requires a lot of effort and additional steps to maintain the information in the step-by-step history. Specifically, they require editing the particular historical step that parameterized the object instead of changing the object itself. This method allows a user to modify a feature of an object only when the object is in the same state that it was in when the feature was created.
Other systems provide the combine and split actions using many different tools, as shown in the representative workflow of some example cases in FIG. 16. Occasional pre-selection is offered, and little logic is performed by the system to determine the user's intention. To select the correct tool, the user must know in advance which objects they want to merge and which tool is appropriate for those objects. In addition, the user must switch between tools when performing the same action (such as a merging) when the target and cutter objects are different types. The entire action must be completed to see the expected result; there is no preview of the appearance of the final object before regions are deleted.